Photoelectric organ



July 27, 1965 R. E. WILLIAMS 3,

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3 Sheets-Sheet 3 3/ i /sa r0 ugly SOURCES R. E. WILLIAMS PHQTOELECTRIC ORGAN ammo/v 7'0 ALL f To LIGHT sou /5/ s70 sw/rcH LIGHT SOURCES July 27, 1965 Filed Aug. 5, 1958 INVENTOR. RICHARD E. [Mu/441s United States Patent 3,197,543 PHOTQELECTREC QRGAN Richard E. Wiiiiams, Fairfax, Va., assignor to Dimension incorporated, Chantiily, Va., a corporation of Maryland Filed Aug. 5, 1958, Ser. No. 753,354 28 Claims. (Cl. 34-128) The present invention relates generally to electronic musical instruments, and particularly to electronic musical instruments which employ photo-electric tone generators.

In principle, photo-electric musical instruments generate tones by utilizing recorded tone or pitch patterns to modulate light passing to one or more photo-electric cells. The tone or pitch patterns may be of variable density or variable area type, and the techniques involved are in some respects similar to those employed in recording and reproducing sound on film. A large number of systems have been conceived in the past for generating photo-electrically the large number of tones required in commercial electronic musical devices, and a wide variety of techniques have been developed for this purpose. For example, pitch or tone discs have been employed. Such discs are usually entirely clear or translucent except for the presence of a large number of opaque waveform patterns existing in concentric bands on the disc. If a narrow beam of light is focused on one of these bands as the disc rotates, and if a photo-electric tube is placed on the other side of the disc to intercept the light, light passing through the bands is modulated by the variations of opacity of the band, and the amount of light reaching the photo-electric tube varies in accordance with the area of clear hand between the light source and the photo-electric tube. Accordingly, the phototube output current varies in exact accord with the shape of the opaque wave form pattern. if the disc is turned at a sufiiciently rapid rate so that the variations of photo-electric tube current occur at an audio rate, the output current from the tube may be amplified and acoustically radiated. Key controlled systems may be provided for selectively illuminating several bands of pitch tracks, 0 that by suitably manipulating the keys musical selections may be generated.

The problem then arises of making the pitch tracks re-entrant, i.e., inscribing or recording on the pitch disc tracks wherein the total number of cycles per track is so related to the length of the track that an integral number of cycles is recorded on each track. This is extremely difficult of accomplishment because the ratio between adjacent frequencies in the tempered scale varies as the twelfth root of two, and because the accuracy with which frequency must be reproduced in electronic musical instruments is better than 25% for the average human ear, and is approximately .1% for the trained musical ear.

In order to generate re-entrant pitch tracks which have the required frequencies it had heretofore been found essential either to utilize extremely long tracks, which cannot be recorded on discs of reasonable size, or to utilize separate discs for tones of different nomenclature. it might appear that a relatively small disc could contain a large number of tracks provided a sufficiently large number of cycles of approximately correct frequencies were recorded on each track, and that the tracks may be then made re-entrant without appreciable error in tone frequency. This turns out to be an inadequate solution, because the problem is then introduced of illuminating 3.,l7,543 Patented July 27, 1965 the tracks with a beam of light which is sufficiently narrow in the direction of track length that a very small fraction of a cycle is illuminated at any given instant of time, and yet to provide sufficient light at the photoelectric cell to rise above the noise level of the circuitry involved. This proves to be impossible unless a small number of cycles of tone per track is employed, and this difficulty is sometimes described as resulting from a low light storage index.

Still a further problem relates to the speed at which the disc may be rotated. If the disc is rotated with sufficient slowness, a relatively small light storage index may be employed and accordingly a relatively large number of tone cycles per track may be employed. However, when this is attempted problems of controlling and rendering uniform the rotation of the tone disc exist because of the extremely low momentum of the mechanical system. Any slight inaccuracies or non-uniformities of pitch track rotation rate become accentuated audibly, and in practice this approach has been proven to be totally unsuccessful.

The usual solution attempted has been to provide plural tone discs, one for each note of a given nomenclature, and to gear these tone discs together so that they rotate at the appropriate speeds. Thereby each tone disc must be associated with a photocell, and since there are twelve notes of different nomenclature in the evenly ternpered scale, twelve discs and twelve photocells are re quired, in addition to appropriate gearing systems. The system then becomes cumbersome and expensive to build and is believed to be commercially impractical.

The present invention provides a photoelectric musical instrument which employs a single tone disc, which rotates at a convenient speed, which provides for an adequate light storage index, and which permits the recording and reproducing of an extremely large number of tone tracks. :In a practical embodiment of the present invention a total of sixty-one tracks have been recorded on a tone disc having an outer diameter of approximately 10" and an inner diameter for the innermost tone track of approximately 2". Relatively small numbers of tone cycles .per track are employed, yet the tracks are all reentrant.

The present invention makes use of two psychological manifestations in human hearing to circumvent the limitations and problems which have been above indicated to exist in the art, and thus to enable use of a single relatively high speed pitch screen for modulating light. It will be clear as the description proceeds that the priciples of the invention may be applied to magnetic recording systems, in which pitch tracks on magnetic tape or drums are reproduced, as well as to photoelectric systems. For purposes of illustration of the principles of the invention in its broadest aspects, and further to indicate how a preferred form of the invention may be practiced, the system is described as photoelectric.

In accordance with the present invention satisfactory pitch is obtained through synthesis of tones, partial by partial, wherein each recorded partial is the nearest reentrant frequency to that frequency which is commonly accepted by the human ear as true, in the evenly tempered scale. A cyclic speed for the pitch track is selected which is equal to a vibrato frequency, and in the presently described embodiment of the invention, a pitch screen speed of 6.5 r.p.s. is employed. On that basis every recorded tone is recorded at a frequency equal to an integral multiple of 6.5 r.p.s., despite the fact that this procedure leads to inaccurate recording of specific pitches. For example, if tone pitch D2 (73.42 c.p.s.) is to be recorded in re-entrant form, according to the present invention, the correspondence of Table 1 would pertain.

The table shows fundamental and harmonic frequencies to the sixth harmonic, lists the true frequencies to the second decimal place, lists the re-entrant frequencies which are utilized in accordance with the principles of the present invention, and in the last column lists the percentage errors which occur. Generalizing, it is seen that a complex tone including the D-2 fundamental and its second through sixth harmonics is made up of the six partials enumerated in the table. Each partial has a common factor n that is multiplied by a further factor In, dependent upon the selected partial. For the example given, n. =6.5 and m=11 for the fundamental; for the second through sixth harmonics of D2; m respectively equals 23, 34, 45, 56 and 68 to obtain the re entrant record having the ercent error given in the table. We note that for the case specified the fundamental frequency is in error by 2.6%. However, the other components of the complex tone are some above and some below the true frequencies, and because the. entire synthesized tone consists of components distributed both above and below their true counterparts, the error in general decreasing as the order of the harmonic increases, the effect of the total complex is, to the ear, an accurate tone. The maximum frequency error is 6.4/2=3.25 c.p.s On a percentage basis this error is considerable for the fundamental frequency, but becomes geometrically minor at the higher comparative frequencies.

It has been shown in Psychology of Music, by Seashore, published by McGraw-Hill Book (10., pages 60 and 61, that pure sine Waves can be as much as 5% in error in pitch, without the error being perceptible to the ordinary human ear. Since each partial, in accordance with the present invention, is, in fact, a sine wave, the ear tends subjectively to create a fundamental at an approximate sub-multiple of each of the partials in the tone, without objecting to the error which exists in any individual partial. The situation can be likened to a series of experimentally plotted points on a graph, whose locus is approximately a straight line. As the ear attempts to create a fundamental for each of the partials, some of which are above and some of which are below the true fundamental frequency, the subjective effect becomes one of correct pitch.

it is further to be noted that true pitch to the human ear is not necessarily precisely the same as pitch according to the equally tempered scale, since the human ear tends to want to hear low notes flat and high notes sharp. Choice of re-entrant frequencies to be utilized in practicing the present invention may take this factor into consideration.

It may further be noted that if the sum of the reentrant frequencies is added and if the sum of the true frequencies is added, from Table 1, that the total difference between the sums is negligible. The sum of the true frequencies for example is 1541.8 while the sum of the re-entrant frequencies is 1540.5. average frequencies in each case are indistinguishable even to the expert musician.

The second major psychological manifestation which is utilized to advantage in the practice of the present invention is that of vibrato. Scattering of partials as described above could under certain conditions give rise to Accordingly, a

objectionable beats, since the ratio of adjacent partials is not always harmonic. However, by choosing a pitch screen rotation rate which falls within the vibrato range, i.e, approximately 5 to 8 c.p.s., all beats which are generated also fall within the vibrato range as a fundamental, and are manifested to the human car as vibrato effects in the generated tone. By experimentation with various vibrato rates, 1 have found that the vibrato rate of 6.5 c.p.s., i.e., a disc speed of 6.5 c.p.s., is particularly effective in minimizing pitch errors within the vibrato range.

The utilization of a 6.5 c.p.s. rotation rate for the pitch disc has a further advantage, which is that any rotational vibration of the disc speed during a cycle manifests itself as a vibrato effect. it proves to be quite difficult to maintain the rotation of the disc completely accurate, where the accuracy required is of the order of .1% unless rather complex expedients are resorted to.

in accordance with the present invention the disc may be rotated by a good quality motor, and without more, adequate speed regulation of the disc is attained since any variations of speed during a cycle do not produce unpleasant effects on the listener.

A further problem which exists in the production of photoelectric organs relates to the complexity of the optical system employed. Many systems which have been conceived in the past employ relatively long light paths, or complex lenses, or reflectors. These may readily become maladjusted and in addition are relatively expensive to fabricate. The problem of selecting tone track in a ,tone wheel having a great number of tracks without introducing optical or mechanical complexity is one of the serious problems which has heretofore prevented the tie velopment of a practical photoelectric organ. Not only may the tracks be quite narrow, but the distance between tracks may be still narrower. The total amount of light falling on each track must be approximately the same as for any other track, or different notes will have different amplitudes when acoustically transduced. it is necessary that the light beams relating to each track remain relatively symmetrical with respect to the track as the track rotates. It is further necessary that if the beams diverge in cross-sectional area after leaving the track and on the way to the photocell, approximately the same area of the photocell will be illuminated by all the tracks, since otherwise again different notes will have different acoustic amplitudes.

in accordance with the present invention the tracks are selected by means of light bulbs individual to the tracks. In order to illuminate each track an energizing circuit is provided to energize a specific light bulb associated with that track. The light bulbs are mounted on a plane plate behind slits. They are adjustably mounted so that small mechanical motions of the bulb will be permitted for purposes of adjustment. Positions of the slits and the sizes of the slots relative to the position of the bulbs are so selected that light from any given bulb can proceed via only one slot and via one track to the photocell. Adjustment of a light bulb with respect to its slit permits adjustment of the amount of light transferred from the bulb to the photocell and also per- 'mits adjustment of the overlie of the light beam on its track and the extent to which the light beam illuminates the cathode of the photocell. It is a simple matter to energize the bulb and thereafter to move same slightly on its adjustable mounting until only a single track generates the tone, and until that tone is of required loudness. It has been found feasible in accordance with the princi ples of the present invention to utilize sixty-one tracks on a single disc, to associate one-hundred and twenty-two different lamps with the sixty-one tracks, (i.e., two lamps per track) and to derive undistorted tone from any one of the tracks by illuminating the corresponding lamp, and this with a minimum of mechanical complexity, by means of a structure which lends itself to economical fabrication, to ease of maintenance and to freedom from maintenance requirements Well as to ease of adjustment of the system during manufacture or thereafter, in respect to obtaining pure tones of desired amplitudes. The system, While accomplishing these objectives, requires no lenses and no reflectors in the optical system.

Some assistance in providing pure tones without intermodulation between tracks is accomplished by the method adopted for grouping the sound or pitch tracks on the disc. In accordance with the present invention pitch tracks of the same nomenclature are immediately adjacent each other. Between groups of tone tracks relating to a given nomenclature a relatively large space is left, following which appear tones of another nomenclature. In this way, if there is some intermodulation by reason of the fact that light from one bulb impinges totally on one track and to some degree on an adjacent track, intermoduiation is harmonic in nature and, therefore, is not unpleasant and does not detract from the musical quality of the instrument.

According to another feature of the present invention, the photocells employed in the track reading system are off-centered with respect to the disc, whereby two photocells may be employed which are independently illuminated by separate sets of lights, but via the same sound tracks. Accordingly, each sound track is doubly employed. This expedient is of particular value in two manual organs for example, in which case the same sound track may be employed for generating sounds relating to both rnaunals, but each manual may utilize a different set of lights and a different photocell. Maximum manuals utilized in organs of conventional character employ sixty-one keys. Accordingly, by means of this expedient it is possible to employ one-hundred and twenty-two lamps, sixty-one per manual, sixty-one sound tracks on a single disc, and two photocells, by means of WllCh the separate manuals may be completely independent of one anot er except for the duplicate use of tracks. in the two manual system, the separate photoelectric cells are connected to separate pro-amplifiers and separate sets of formant filters, the outputs of which are applied directly to a power amplifier and a transducer. A variety of modifications of the basic organ may be employed: For example, keys may be interlocked, so that when a key of a given nomenclature is depressed, the lrey of corresponding nomenclature out an octave higher may also be depressed, thereby enriching the generated tone. On the other hand a given tone may be coupled in this Way to a tone which is an octave below or above the primarily desired tone. This is equivalent in organ terminology to coupling in a four foot or sixteen foot rank to an eight foot ranlr.

Moreover, a separate switch may be connected in circuit with each bank of keys so that, again adopting pipe organ terminology, the depression of a key of given nomenclature and of eight foot rank may actually sound a tone of four foot or sixteen foot rank and in that same nomenclature. By extending this technique, a basic tone generator can provide two foot, four foot, eigr foot, sixteen foot, ten two-third foot, etc., tones at the will of the player, since the precise jump employed need not be precisely octaval.

in accordance with still another modification of the present invention, which lends further flexibility to tone color generation in a system having a single tone generator and two keyboards, electrical coupling may be provided between the switches while the total tone amplitude generated with or Without coupling is the same. In accordance with this technique, like sources are borrowed by one or more keys in such fashion that as more keys borrow from the same source, its intensity increases as if new sources were being added.

According to a further feature of the invention, correction is made for the fact that each light bulb is at a different distance from its associated track and from its associated photo-cell. This fact, taken in conjunction with the further fact that light diminishes in intensity as a function of distance from its source according to a square law, leads to certain difiiculties. The intensity of light falling on any track is different from the intensity of light falling on other tracks, and the decrease in both intensity or" light and in divergence of light beam in passing from a track to a photo-cell is also different for each track. There being no optical devices for condens ing light in the present system, these effects cannot be optically compensated. The difficulty is increased by virtue of the locations of the several tracks radially, as a function of pitch, i.e., adjacent tracks do not represent adjacent pitches, but represent octavally separated pitches. The difference in li ht intensity for pitches of adjacent ctaves may, therefore, be slight, but the difference for adjacent pitches may be considerable and quite noticeable, and it is difficult to compensate by adjusting lamp positions.

In accordance with the present invention compensation for differing distances from lamp to tracl; to photocell is accomplished by constructing the tone disc so that the degree of modulation employed is a function of distance of the track radially from the center of the pitch disc, or that track Width increases as a function of radial distance. Since, moreover, five groups of pitch tracks are employed, each containing twelve tracks, to handle sixty keys, it is feasible to maintain track-width or modulation depth constant Within each group and to make adjustment only for the several groups. This simplifies fabrication of tone discs in that only twelve dilferent modulation depths or traclrwidths are required.

Still another problem which has plagued those working in the field of photoelectric musical instruments is the problem of dust. In systems which employ slowly rotating pitch discs, or stationary pitch discs and slowly scanning slits, dust collects on the disc and in the slits. Collection of dust in the slits is equivalent in effect to providing slits which are not sharply defined, which leads to some tone degeneration. H Wever, dust on the tone traclrs introduces high frequency noise into the system, at high level, and his presents an extremely serious problem.

Attempts have been made to reduce dust colle ction by enclosing tone discs completely. This represents an expensive expedient, and moreover, it has not proved successful in practice.

According to the present invention collection of dust is completely prevented by virtue of the high rotation rate of the pitch disc, and further because an electrically grounded metallic plate is closely adjacent to the pitch disc, the latter being glass. It is found that dust collects on the pitch disc only while the pitch disc is stationary. As soon as it commences to rotate at 6.5 c.p.s. the collected dust is impelled outwardly of the disc, where it tends to collect on the periphery, and inwardly of the disc where it tends to collect on the disc drive shaft. I explain this as occurring because a potential gradient is set up radially of the disc by virtue of friction with air, and by virtue of the fact that the circumference of the disc is the fastest moving element of the disc and hence acquires the highest potential. The slit plate is spaced from the disc by slightly less than A and is grounded and metallic. A relatively high potential gradient then exists from disc circumference to slit plate, and the dust, when it has acquired the charge existing at the circumference of the disc, is repelled by the disc and attracted to the plate. The latter is greater in diameter than the disc, so that the dust collects on the plate only outside the area of interest.

I have, therefore, provided, not only an effective dust removal system, but one which is inherent in my system, and which requires no added elements for the purpose.

It is, accordingly, a broad object of the present inven tion to provide a novel electronic musical instrument.

it is a further object of present invention to provide a novel musical instrument of the electronic organ type.

Still another object of the invention resides in the provision of a novel photoelectric organ.

A further object of the invention resides in the provision or a photoelectric organ employing a single tone disc for generating a complete complement of organ tones.

Still another object of the invention resides in the provision or" a photoelectric organ which employs no lenses or reflectors.

A further object of the invention resides in the provision of a photoelectric organ employing a single sound disc and two photoelectric cells energized by light passed through the sound tracks on the disc, in such fashion that a single sound track may energize either or both photoelectric cells.

Another object of the invention is to provide a novel method of preparing pitch discs for photoelectric organs.

nether object of the invention is to provide pitch iscs having tone tracks of complex character, partial which are selected in accordance with a novel so that all partials will be rc-entrantly recorded. 1 another obiect of the invention is to avoid errors in fabricating pitch discs of complex nature, by preliminarily recording desired complex tones on a magnetic tape recorder, and thereafter transducing these complex tones to a pitch disc, thereby deriving the advantage that the tones may be listened to prior to recording thereof, and if any synthesized tone is in error or unpleasing for any reason, it may be erased and resynth-esized.

A further object of the invention resides in the provision of a single mechanically simple assemblage for interrelating tone discs, light sources, photoelectric cells and light apertures in a small, compact, light unit having no re ctors and no lenses and which permits selection of any tone track at will.

A further object of the invention resides in the provision of a sin le, compact, economically fabricated tone generator, comprising a single tone disc having multiple tracks thereon, including tones extending over plural octaves, wherein tones of the same nomenclature are recorded in adjacent tracks and wherein groups of tones of given nomenclature are separated from groups of tones of any other nomenclature by a relatively large space on the pitch disc.

Another object of the invention is the provision of a photoelectric tone generator employing a single tone disc, two photocells and two light assemblages, the light generating assemblages consisting of arrays of light bulbs, any single track being shared by two lights, each of which may be connected to a key of a different manual of he organ.

A further object of the invention is to provide novel evices for coupling tones in photoelectric organs, so that tone of eight toot rank may be coupled with a tone of sixteen foot rank, or of tour foot rank, or in general of another ranlr.

Another object of the invention is to provide novel systems for obtaining octave coupling in the tone generator of a single disc electronic photoelectric organ.

Still another object of the invention is to provide essentially independent tone groups to two keyboards of an organ from a single photoelectric tone generator.

Another object of the invention relates to a tone disc for an electronic photoelectric organ wherein the tone tracks are related to the ""e of rotation of the pitch disc and where in that of rotation falls within the vibrato frequency range, or is the vibrato frequency employed in the instruinent.

it is still another obicct of the invention to provide a tone generation system of the photoelectric type, in which a disc is employed which is fabricated of dielectric material having a different dielectric constant air, and the circumference of which moves at a sufii i 1 tangential velocity that a potential gradient liy of the disc which is of magnitude great gli to clean the surface of the disc of dust. cll a further object of the invention resides in the pro vision of a tone disc in which depths of modulation of the s are selected to compensate for dif- ""ht s from light source, to pitch fora pitch track to photocell, for the separate rate s YClalfl embodiment thereof, especially when tairen in contion with the acconoanying drawings, wherein: Fill-U213 l is a block diagram of a system for fabricatdiscs for a photoelectric organ, in accordance present invention;

is a circuit of part of an electric god in accordance with the present invention;

chanical assembly of a pitch disc, lamp aggregate and photocells arranged in accordance with the present invention;

FlGURE 4 illustrates in schemati circuit diagram elediagram still p"ovide rank coupling;

8 is schematic circuit diagram of. a system for extending the use or" available stop filters in an electric organ; and

FIGURE 9 is partial sectional view taken transversely or" a slit plate, and showing the construction.

Referring now more particularly to FlGUR-E 1 of the accompanying drawings, i will provide exemplary plura lity of precision oscillators, identified by the reference Each of these oscillators is oper tive over the audio range, i.e., from about 20 c.p.s. to aoout 18,600 cps, and may be manually adjusted with over ccnsi arable periods of time. The precision oscilusive, supply signal across potentiometers inclusive, each of which is provided with an out- 'l sliders are connected respectively in series with isolating resistances 9 to 1 .2, inclusive, each of which a common line 13 to a combining resistance 3 is connected directly to the input of an am the output of the latter may proceed to a magnetic tape recorder and reproducer ltl.

The total number of precision oscillators (similar to oscillators to i) which may be utilized in a given operation is a matter of choice. in general, more than four .tors will be employed to produce a pitch track. However, illustration of additional oscillators appears to be unnecessary for the explanation of the principle of the invention, and is accordingly, dispensed with.

A precision frequency meter 17 is provided, the input circuit of which proceeds to a switch 18, having a wiper arm 19 and multiple contacts 2%. The separate contacts 2d are connected individually to the ungrounded sides of the potentiometers 5 to S, inclusive. By setting the'wiper arm 19 to any separate contact 29, the corresponding oscillator will be connected to frequency meter 17, making it possible accurately to set the frequency of the oscillators to frequency values suitable for a given pitch track. These values are calculated in advance, according to the musical character desired for the tones. Having set the oscillator frequencies, in accordance with the previously planned schedule, amplitudes of the oscillator outputs as seen at the amplifier T5, are selected by adjusting the sliders of the potentiometers 5 to 3, inclusive. Each one of the oscillators provides one partial of the synthesized pitch track, which includes a fundamental, preferably provided by the oscillator l, the partials consisting of re-entrant frequencies, based on a common multiple of 6.5 c.p.s. By properly selecting the relative amplitudes of the partials a wide variety of musical tones may be synthesized.

Each synthesized tone may be applied to the recorder of a speed adjustable magnetic tape recorder and reproducer id, for recording thereby in response to closure of a switch 21. Reproduced synthesized tone may be derived from the output of the magnetic tape recorder and reproducer re via a switch 22, at will. If desired, how ever, the switches 21 and 22 may be opened, disconnecting the recording and reproducing portions of the recorder and reproducer is, and the outputs of the amplifier 3.5 may be applied via a switch 23 directly to a lead 24.

There then appears on the lead 24, either directly from the amplifier or from the reproducer section of the recorder and reproducer 16, as the case may be, synthesized tones having the character appropriate to fabrication of tone discs in accordance with the present invention. Frequency of output from the tape recorder must be hecked against frequency meter 17, and speed of the reproducer adjusted, since tape stretching can introduce significant inaccuracies.

A turntable 25 is provided, which is rotated at constant velocity by means of a synchronous AC. motor 26. The motor 26 is driven at adjustable speed from a motor drive source 27. The motor 26 being preferably a synchronous motor, the voltage provided by the source 2'7 is a frequency controllable voltage. Voltage supplied to motor 26 is also supplied via a lead 28 to one of the contacts ill of the switch 18, and thereby to precision frequency meter The speed of rotation of the turntable 25 may be thus adjusted very precisely, and in a preferred em bodiment of the invention is set at a frequency of 6.5 c.p.s. It is found in practice, however, that household current has the requisite frequency accuracy and stability, without adjustment, in most locals. The frequency of 6.5 c.p.s. herein referred to, is a selected vibrato frequency in the present invention. It has been found experimentally that this vibrato frequency operates exceptionally well. Nevertheless, it is appreciated that other vibrato frequencies may be used, such as 7, 8 etc., c.p.s. But in each case the basic frequency factor of the several precision oscillators 1 to d, inclusive, must also be the same factor. It

. is an essential feature of the present invention that the rate of rotation of the turntable 25 be precisely related to the basic frequency component of each of the several oscillators l. to d, inclusive, as an integral sub-harmonic thereof, and that at the same time it be used as the vibrato frequency of the system. An explanation of the relation of the partial frequencies to the vibrato frequency employed has been provided hereinabove and an example has been provided of numerical values of frequency suitable for a given synthesized tone.

it will be observed from the table that the so-called reentrant frequencies are integrally divisible by the selected ill vibrato frequency, i.e., 6.5 c.p.s. It is not essential that harmonic relations exist among the partials comprising a synthesized tone. Where harmonic relation is departed from, however, the partials depart from harmonic relation by the addition or subtraction of a factor 6.5 c.p.s. Use of the precision frequency meter 17 is, accordingly, to relate the frequencies of the oscillators 1 to inclusive, and the rate of rotation of the turntable 25, to the basic value 6.5 c.p.s.

When the precision oscillators 1 to 4-, inclusive, and the potentiometers .5 to 23, inclusive, have been set up for synthesizing a tone, a switch 29 is closed, which energized a timer 3b. The timer 30 supplies current to a lamp 31 for a predetermined time interval appropriate to the tone being generated, and the timer 3%) is turned 013? at the end of the predetermined interval.

The lamp 31 supplies light to a galvanometer type light modulator 32 which is supplied with current from the lead 24. The galvanometer 32 vibrates in a direction radially of the turntable 25, so as to generate a variable width recording, and supplies light through a collimating element 33 to a photo-sensitive disc 34 resting on and rotated by the turntable 25.

The several pitch tracks which are to be fabricated each occupies a different radial position on the photosensitive disc 34-. The radial distances are selected by moving the light source 31, the galvanometer C32, and the colimating element 33 together, as a unit, on a threaded shaft by means of a hand crank 35. The galvanometer 32. and the light source 31 may be included in a light proof box 37, while the photo-sensitive disc 34 and associated apparatus is included in a light proof container operation, then, a schedule is set up for the values of frequencies and amplitudes of the several partials of a tone which it is desired to synthesize and record. The crank 36 is adjusted so that a recording will take place at an appropriate radial position of the disc 34. The switch 29 is at this time open, so that the lamp 31 is deen rgized. The switch 19 is thrown to the contact 20 of switch 13 which is appropriate for measuring the output frequency of the photo-drive voltage source 27, and the latter is adjusted to be precisely 6.5 c.p.s. The wiper arm 19 of the switch 13 is then applied in turn to the separate contacts 2% of the switch 18, and at each of these the appropriate precision oscillator of oscillators 1 to 4, inclusive, is adjusted as to frequency by reference to the precision frequency meter 17, so as to have the correct re-entrant frequency for the synthesized tone, i.e., a frequency equal to an integral multiple of 6.5 c.p.s. but adjacent to true value for the partial. The several potentiometers 5 to S are then adjusted to provide the proper amplitudes for the several partials. When this has been accomplished the switch 21 is closed and a recording made on magnetic tape of the synthesized tone. This tone is then reproduced by means of loudspeaker it? so that it may be examined aurally for correctness of tonal character. Should there have been an error made in selecting the frequencies, setting the sliders of potentiometers 5, or the like, the resulting tone will have an undesired character, and it Will be possible, in general, aurally to detect or to recognize that an error has been made. In such case, the tone may be erased from the magnetic tape, the settings of the oscillators, and of the motor speed may be rechecked, and the tone may be rerecorded in synthesized fashion. When the listener is satisfied with the character of tone, the switch 22. may be closed so that the synthesized tone may be applied to the galvanometer 32. In this condition of the apparatus the timer Ed is set for an appropriate time and the switch 2? closed. Thereby the lamp 31 is turned on, illuminating the galvanometer 32 and effecting the recording of the pitch track. Thereafter, the crank 36 is adjusted to a suitable radius for the next synthesized tone and the operation is repeated.

The combined outputs at the slider 91 are applied to a power amplifier 92 and thence to an acoustical radiator 93, such as a loudspeaker. To the amplifier 92 is also supplied vibrato modulation deriving from modulator 9 5, which modulates the frequency of output of the amplilier 92 at a vibrato frequency equal to 6.5 c.p.s. in the present system. It is important to note that the vibrato rate employed is equal to the rate of rotation of the pitch disc 34. It follows from the manner in which the synthesized tones were synthesized and from the rate of rotation of the pitch disc 34-, that slight variations of rotational velocity of the pitch disc 34 appear to the ear as vibrato or tremolo effects, and they therefore are not displeasing and in fact accentuate the pleasure derived from listening to the organ.

Reference is made to FIGURE 8 of the accompanying drawings, wherein is illustrated as a schematic circuit diagram, an improvement of the system of PEG- URE 2, wherein the outputs of the manuals A and B, pro-amplifiers ill, 83 are applied to separate cathods follower stages 95 and 96, from the cathode loads 97 and of which may be taken output for application to either of the A manual or B manual formant filters, 84, 87, by means of appropriate switches E39, 1%, lldl and lltlZ. For example, output from pre-amplifier 81 which is responsive to manual A of the organ, may be applied to the manual A formant filters via switch 99, or to the manual A formant filters when switch 1% is closed or to both the manual A and manual B formant filters when switch 99 and 1% are both closed. Likewise, signals taken across cathode resistances may be applied to the manual A formant filters 554 when switch Trill is closed, to the manual B formant filters 87 when switch W2 is closed, or to both sets of formant filters when switches 1M and 162 are both closed. Thereby, each set of formant filters is made available to both manuals, i.e., the formant filters may be interchanged so that the A formant filters may be used for the B manual, and the B formant filters may be utilized for the A manual, interchangeably, or a given set of formant filters may simultaneously become responsive to both manuals. Obviously, anode loaded tubes may be employed instead of cathode coupled tubes, as desired.

Reference is now made to FIGURE 3 of the accompanying drawings, Where is shown in some detail the structural features of the light modulating assembly of the system of FIGURE 2, and wherein is particularly specified certain dimensional arrangements which are important to the successful practice of the invention. it may be noted by reference to FIGURE 3 that a given track, as 65, on the pitch disc 34, is at a smaller radius than is the slot, as 63, pertaining thereto, which is in turn at a smaller radius than is the lamp, as 61, pertaining to that slot. it will further be noted that the photocels 66 and d7 are on alternate sides of a line running through the shaft 51 and that they are separated by means of an opaque plate lllii which mutually isolates the photocells 56 and 67 from the separate groups of lamps pertaining to the manuals A and B.

The lamps all are mounted on a plate llll, which re mains stationary during operation of the system, as does the slit plate 64, and each lamp is mounted on a bracket, as 112, which is shown illustrated for the sake of example only, in the form of L-shaped brackets. The brackets 112 are sufficiently soft and resilient so that they may be bent radially and circumferentially on application of a reasonable force, whereby the position of each lamp circumferentially and radially may be slightly adjusted. The actual shapes of the brackets 112 are not a matter of moment, so long as each bracket is riveted or otherwise firmly connected to the plate ill at one of its arms and so long as the lamps are secured as by soldering or brazing to another arm, and so long as the arm to which the lamp is secured may be adjusted both circumferentially and radially. The application of it"s: suitable forces to the brackets may be effected manually by a pair of pliers. Once adiusted, of course, the brackets must retain their positions despite the shock incident to normal shipping and use of the equipment.

Similarly, the lamp mounting plate llll must be fabricated of relatively heavy metal, so that it will not become deformed due to inadvertent shocks or pressures.

It has been found that a mathematical relationship exists among the various dimensions pertaining to the structure of FlGURE 3 of the drawings, and particularly the following:

R equals radial distance to light source from motor axis;

A equals distance from slit screen plane to light source plane;

equals distance from photocell plane to slit screen plane;

T equals radial distance from motor axis to sound track center;

p equals the radial distance from motor axis to light sensitive cell center; and

(p erg-sis the angle between the light source radial and cell axis plane.

The formula connecting these quantities is as follows:

The distance from the pitch disc 34 to the slit disc 64 is between .05" and .020. The width of the various slits 63 is made as small as possible consistent with adequate light storage index, and the height of the slits (.050") is selected to provide complete illumination of one track from the appropriate lamp, without overlap to adjacent tracks, or without substantial overlap to adjacent tracks.

it will be observed that the distance from any given lamp to the slit appropriate to a given pitch track is not a constant for all the lamps. Since light diverges, it follows that the radially outermost tracks are subjected to smaller strength of light beam than are the innermost track". This cannot be readily or rapidly compensated for by the adjustment or selection of the lengths of the slits, although it can be done. it is, furthermore, the case that light passing from a given pitch track to a photocell follows a longer path for the pitch tracks of greater radius, and consequently that a light of greater cross-sectional area but smaller intensity falls on the photocell when that light is derived from a pitch track of greater radius than when that light is derived from a pitch track of smaller radius. in balance, these various effects result in the consequence that tracks at greater radii illuminate the photocell with a smaller quantity of light than do tracks of lesser radius. This effect might be com ensated for in many ways.

For example, the intensity of illumination of the appropriate lamp may be adjusted, or the lamps positions may be adjusted by bending the brackets llZ so that the amount of light passing through a given slit to the track and thence to the photocell is reduced or enhanced, as re quired. All these possibilities do exist, but involve economic factors that are disadvantageous. In accordance with the present invention, compensation is effected by selecting track widths and track modulation depths so as to compensate for the various factors which have been above described. By adopting this expedient it is feasible in fact to utilize lengths of light slits 63 which are uniform for the entire disc, and to minimize manual adjustments, and this in turn reduces the cost of fabricating the slit plates. in practice, noreover, where identical slits are utilized for all the lamps and all the pitch tracks, and where compensation is effected for lengths of light beams and for'angular spread of light beams, by suitably adjusting the modulations on the several pitch tracks, such compensation may be approximate, since ultimate adjustment of the system in respect to generating tones of equal intensity in response to depression of the several (eys of the several manuals may b ment of the positions of the lambs,

necessary, and which may be accomplishc terms of lamp positions.

in respect to adjustment of lamp position, it may be noted that circumferential adjustment affects variation of the quantity of light which reaches a pitch track, while radial positioning of the lamp is required to assure that light from each lamp is modulated by only a single track.

it has been found that if the slit plate 6 3- is fabricated by punching out slits in a relatively thin sheet of metal, that the thin sheet of metal has inadequate mechanical strength to withstand inadverent shock or careless handling. On the other hand extreme difliculty is encountered in fashioning clean slits by punching relativel' heavy sheet metal. I have, accordingly, adopted the device of l lGUiE 9 of the accompanying drawings, wherein the slit plate 6 is pro ided with relatively large apertures loo, which may circular if desired, over which is placed thin brass shimstoclt, as uIt, the apertures, as as, being punched in the latter and the openings being sufi'iciently large that they do not interfere with light passing through the aperture 63. it has been found possible to punch extremely clean, accurate slits having very narrow width and considerable lengths, in such shimstock. Accordingly, in fabricating a slit plate, slits are fern -d in a strip of s ustocic, eihaps /4 inch wide, at positions appropriate to one radius of the slit disc, and the shimstoclc is then secured to the main plate as by soldering or brazing. This permits the use of very heavy stocl; on the main plate 6d, so that the positioning of the slits will not be effected by careless handlin of the equipment or by inadvertent shocks applied thereto, while simultaneously facili ating the punching or extremely clean slits, free of burrs, rounded corners, and the like.

Reference is now made to FIGURE 401" the accompanying drawings, wherein is shown a system for rank coupling in electronic organs of the photoelectric type. In the system of FIGURE 4 a source of voltage V is connected at one terminal to the common terminals of a plurality of light sources (as at, 62 of FIGURE 2). The other terminal of the source V proceeds via a first stop switch 154) to a plurality of parallel switches which are labelled A A ii and B and via leads 151, E52, 153 to appropriate light sources in the system of FlGURES 2 and 3. A further stop switch 155 is connected in parallel with the stop switch 1&8! to a series of parallel connected switches labelled A Al B which in turn connect with leads 156, id? and 158 connected to appropriate light sources 62. The designations of the switches indicates the nomenclatures of the tones which are generated when the switches are closed and the light sources accordingly energized. The switches A and A are mechanically ganged so that they are opened and closed together. A similar condition exists for the switches Al and Al and the switches B and B it may be assumed for example that A is either an octave lower or an octave higher than A or more generally that there exists a musical relation therebetween, so that closure of both switches results in a pleasing tone which is enhaiiced with respect to the tone which might be obtained were only one of the switches closed. it now follows that it the stop switch 15%? is opened, that only the light switches A Al and B are effective, while if switch 155 is open and switch ft? is closed, only the switches A Aii and B are effective. n the other hand when both switche are closed, both A and A are simultaneously generated, or tones Al and All are simultaneousy generated, or tones A and A are simultaneously generated. Accordingly, by selective actuation of the stop switch 153 and 1155 a selection of three different tone characters becomes available. This is equivalent in organ terminology to coupling in the four foot or sixteen foot ranks of pipe to an eight foot rank. It will be apparent that by a simple rearrangement of switches the basic tone generator can provide two foot, four foot, eight foot, sixteen foot, ten /2, foot, etc, tones, at the will of the musician, since the techniques need not be limited to the precise octave jumps suggested. For example, closure of switch 159 may result in generation of four toot tones 10 while closure of switch 155 results in generation of eight foot tones. Closure of both switches then results in both a four foot and an eight foot tone in response to actuation of a single key.

The system of FlGURE 4 results in increased tone amplitude when both switches and 155 are closed,

not) since actuation of a single key results in illumination of two lamps. Reference is made to FlGURE 5 of the accompanying drawings, wherein is illustrated schematically a variant of the system of FIGURE 4. In the sys- 29 tern of FIGURE 5 there are shown six lamps, pertaining to tones Ch, D C CiE D The subscripts indicate the octaves within which the tones falls, so that three lamps are indicated which pertain to one octave and three further lamps which pertain to an octave above the first octave, for example. Switches are illustrated, which may be operated in pairs from a single keyboard. A first set of switches is identified by the reference numorals 2%, 2591, 232, 2%, 2M and 2955. A second set switches is identified by the reference numerals 2%, N7, 238,269 and 2M and 2111. Battery V is connected to the first set of switches in parallel by means of a stop switch 155, and to the second set of switches 295411, inclusive, in parallel via a stop switch 150. Either or both sets of switches may be connected in circuit according to the stop switches which are selected. Assuming that the stop switch 155 is open and the stop switch 15% is closed, I direct attention to the D D lamps. In such case closure of the 2&8 switch energizes the D lamp through impedance 2% which is in the form of a resistance having a value such that the D lamp provides half its normal illumination. Switch 2% is mechanically ganged with the switch 295 which supplies current to the D lamp. When the stop switch 156; is open and the stop switch 155 is closed, the D lamp becomes energized through a resistance 221, having a mag nitude such that the D lamp operates at half normal brilliance. It then both stop 156 and 155 are simultaneously closed, actuation of switches 2% and 2%, K which are ganged mechanically to a single key, results in illumination of the D lamp at half brilliance and ot the D lamp at half brilliance. While I have mentioned half brilliances as applicable to the illumination of the lamps D and D it will be appreciated that, in fact, this is not a precise description, but that the reduction in brilliance is such as to produce a resulting tone at half normal loudness, which may involve something less than reduction of normal brilliance by one half.

We have now the combination in which depression of a single key may be caused to produce a tone D 01" D according to the stop switch selected, or D plus D when both stop switche are selected.

While the circuitry has been illustrated and described as applying particularly to two tones which are an octave apart, it will be appreciated that this relationship is exemplary only, and that coupling may be effected with respect to other relative tone values, by means of the s 'stem of FIGURE 5, i.e., the coupling arrangement of FIGURE 5 may be extended to include rank coupling between two foot, four foot, eight foot and sixteen foot ranks, or with intermediate ranks.

Still a further modification of the systems of FlGURES 4 and 5 is illustrated in FEGURE 7 of the accompanying drawings. in this system two voltage buses are utilized. 7 A four foot bus, ii, for example, is maintained at ten foot bus, 4 51, is maintained at 6 volts, win

volts, and the latter is maintained energized at all times. The various lamps are energized from the eight foot bus directly, i.e., without the interposition of any resistance, as by means of switches 252 connecting with the C lamp, switch 253 connecting with the E lamp and switch 254 connecting with the C lamp. The four foot bus, 250, which supplies 10 volts, is connected to the various lamps via resistances as 256, 257 and 258. The voltage drop introduced by any of the resistances 256 or 257 or 258, when a lamp is connected, is equal to four volts, i.e., the difference between the voltages of the four foot and eight foot buses, 250 and 251. The switch 252 which controls the C lamp is mechanically coupled to a further switch 260 which controls the C lamp. The switch 261, coupled to the switch 253 mechanically, energizes an E lamp via resistance 257 from the four foot bus 250. A C lamp is also energized via a switch 262 which is mechanically coupled to the switch 255, and the lamp C is energized from the four foot bus via the resistance 253. The philosophy of the system may be explained by reference to the C and C lamps. If the C lamp is directly energized from eight foot bus 251 via switch 254, it is operating at 6 volts. If now the switch 26% is closed, the total voltages applied to the lamp C remains six volts because the lamp C is energized from the four foot bus at 10 volts through resistance 256, which introduces a four volt drop in voltage. It follows that the lamp C may be energized at six volts by closure of switch 254 or by closure of switch 260, and that closure of both of these switches simultaneously does not result in any change of voltage applied to the lamp C and consequently does not result in any change in the brilliance of the lamp. The four foot bus may be selected by means of stop switch 270, but the eight foot bus must be in circuit at all times.

If now we were to mechanically couple the switches 260 and the switch 252, so that both switches were operated in response to depression of a single key of an organ, then we could select by means of the stop switch 270, whether the lamp C alone and both lamps C and C would be operative, on depression of the key, by se lectively closing and opening stop switch 270. Moreover, if switches 252 and 260 were ganged and if the stop switch 270 was closed, energizing lamps C and C these two lamps would both be energized at six volts. If then the switch 255 were also closed, the net result would be application of an additional source at six volts to the lamp C which would not change the current flow through the lamp C nor vary its brilliance. Assuming that switches 255 and 262 were ganged, closure of the key which controlled these two switches would merely add lamp C to those which had been illuminated, so that lamps C C and C would all be illuminated, but all would be illuminated to the same extent, i.e., at six volts.

The system of FIGURE 7 possesses advantages over the system of FIGURE in that the total number of resistances has been reduced by a factor of two. Since there may be a total of one-hundred and twenty-two lamps in a practical embodiment of the present invention, it will be appreciated that this represents a saving of one-hundred and twenty-two resistances plus the saving of the cost of soldering these resistances in the circuit, which represents a considerable economic advantage.

A further advantage is that in the system of FIGURE 5 the matrix resistances typically must be five to ten times lamp resistance, in order that sneak circuits be unavailable for certain combinations of switch closures. Use of such large resistances represents a considerable power loss, and involves using considerably higher voltage power sources for the lamps than these require per se. In the system of FIGURE 7 on the other hand, the values of matrix resistances employed may be a fraction of the lamp resistances. In this system the eight foot bus 251 must always be energized, so that there is always available a six volt potential for purpose of bucking out potentials supplied from other buses.

The principles of the invention of FIGURE 7 may obviously be extended to three or more buses. If, for example, a two foot bus were added, it would be necessary to leave the four foot and eight foot buses permanently on. While I have disclosed the several buses, in the system of FIGURES 4, 5 and 7, as DC energized, it is clear that A. C. may be employed, provided that the frequency of the AC. supply is sufficiently above the audio band.

One of the things which plagues the designer of a photo-electric organ is dust. When such organs remain unused for a period, dust collects on the pitch plate, and unless this dust is removed, it generates noise in the acoustic output of the organ. Attempts have been made in the prior art to avoid the dust problem by sealing the pitch disc in a dust-proof box. In fact, such expedients have failed, because in the course of time some dust has always been able to filter into the dust-proof box and the effect has been cumulative with time.

The present system has been found to be dust free without the use of any expedients for the purpose of removing the dust.

The pitch disc, in a preferred embodiment of the present invention, is fabricated of glass. Glass has a very high dielectric constant relative to air. The pitch disc rotates at 6.5 c.p.s., so that the outer circumference of the pitch disc is moving at a relatively rapid rate, while the center of the pitch disc has no linear velocity. It is found, accordingly, that a very considerable voltage gradient is developed between the outer circumference of the pitch disc and its center. Dust which collects on the pitch disc then acquires a random charge and in response to the potential gradient in which the dust finds itself, the dust moves either toward the circumference of the disc or toward the axis of the disc. The innermost pitch track on the disc is a radius of approximately two inches. Therefore, any dust which moves to the axis of the disc does not affect the operation of the system. Dust which moves to the outer circumference of the disc likewise is not adjacent to any pitch track. Moreover, the slit plate 64 is fabricated of metal and has a greater diameter than does the pitch disc 34. The metallic slit plate 64 is at ground potential and is placed from the pitch disc at a distance of slightly less than of an inch. On this basis a considerable voltage gradient exists between the outer circumference of the pitch disc 34 and the surface of the slit plate 64. When the dust attains the outer circumference 34 of the pitch disc, it also attains the same charge as exists at that point of the pitch disc, and is therefore repelled by the pitch disc toward the slit plate 64, which collects the dust, but at a radial distance sufficiently great that the dust does not affect the operation of the system in any way.

I have advanced a theory which I believe explains the operation of the present system in eliminating the dust problem. However, I do not desire to be bound by this theory, but merely to indicate as a fact, that in a full scale model of the equipment which I have fabricated and tested, dust does not collect on the pitch disc, while the pitch disc is moving, and that such dust as does collect on the pitch disc while the pitch disc is stationary is in fact removed to the outer circumference and to the inner axis of the pitch disc when the latter rotates, and that the dust which moves to the outer circumference is almost entirely collected by the slit plate. The theory which I have advanced is the most logical theory which I have been able to devise for the phenomenon which I have observed, but is not necessarily the only logical explanation nor the correct explanation.

Referring to FIGURE 3 of the accompanying drawings, dust on the circumferences of the pitch disc is illus- 19 trated and identified by the reference numeral 3%. Dust collected on the slit plate 64 is illustrated and identified by the reference numeral Still and dust which has collected adjacent the axis of thepitch disc is illustrated and identified by the reference numeral 3%.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In a system for fabricating a tone disc, a plurality of frequently adjustable oscillators, means for additively combining preselected proportions of the outputs of said oscillators, a frequency meter, means for selectively and at will applying the outputs of said oscillators to said frequency meter for measurement of the frequencies of said outputs, a turntable for rotatably supporting said tone disc, a light modulator responsive to the preselected proportions of the outputs of said oscillators as provided by said means for additively combining, means directing light from said light modulator to from a circular tone track on said tone disc, an A.C. synchronous motor, an A.C. voltage source for energizing said motor, and means for applying said A.C. voltage to said frequency meter at will.

2. In a keyed musical instrument, a single record storing device, said record storing device having recorded thereon a plurality of re-entrant tracks each corresponding with a complex musical tone, certain of said tracks being non-harmonically related, first means for at will selecting and reproducing the musical content of any of said tracks as first electrical signal in a first channel, second means for at will reproducing the musical content of any of said tracks as second electrical signal in a second channel, and means for commonly acoustically reproducing the signal content of both said channels.

1 3. The combination according to claim 2, wherein is provided means for separately and at will modifying the tonal character of said first and second signals.

4. A record receiver having re-entrantly recorded thereon at least one complex musical tone including a plurality of partials, wherein each of said partials is recorded as a plurality of complete cycles equal to nm, where m is an integer diiferent for each of said partials, n is a number less than thirteen and the same for all said partials, and mu is approximately equal to the true frequency of that partial in the musical scale.

5. The combination according to claim 4, wherein n is substantially 6.5.

6. The combination according to claim 4, wherein is provided means for generating frequencies of values mn in response to said recording, and wherein the values of said frequencies lie in part above and in part below harmonics of the true value of the lowest frequency partial.

7. In a system for providing a plurality of complex tonal records on a single re-entrant record receiver, wherein said record receiver has a rate of re-entrant n c.p.s., where n is a number, means for recording each of said complex tonal records as a plurality of partials, and means for selecting the frequency of each of said partials to be mn Where m is an integer.

8. In a system for fabricating a tone disc, a plurality of frequency adjustable oscillators, means for additively combining preselected proportions of the outputs of said oscillators, a frequency meter, means for selectively applying the outputs of said oscillators to said frequency meter for measurement of the frequencies of said outputs, means for adjusting the individual frequencies of said oscillators by reference to said frequency meter to have predetermined frequency relations having a common factor, means for preparing a magnetic recording 22% of the outputs of said means for additively combining, a turnable for rotatably supporting said tone disc, a light modulator responsive simultaneously to the preselected proportions of the outputs of said oscillators as provided by said magnetic recording for generating a width modulated light beam, means directing said light beam to form a circular tone track on said tone disc, an AC. synchronous motor for driving said motor at a frequency equal to said common factor.

9. In combination, a photocell, a modulating element, said element being a single record storing device having recorded thereon a plurality of re-entrant tracks each corresponding with a complex musical tone, a light beam defining device having a slit and a source of light, all in a single plane, and lying in a first rectilinear line from which may be drawn plural perpendiculars to a second rectilinear line, said perpendiculars to said photocell, said modulating element, said slit and said source of light lying at progressively increasing distances from said second rectilinear line wherein said source of light is a lamp having a rectilinear filament extending parallel to said perpendiculars. t 1

16. In a keyed photoelectric organ wherein is provided a plurality of tone generators, at least one for each tone of a plurality of octaves, and wherein each tone generator includes a lamp which effects generation of a tone only when energized, the combination of a separate switch for energizing each of said lamps, each of said switches pertaining to a note of a predetermined nomenclature in a specified octave, means for gauging switches of the same nomenclature, a plurality of keys each for actuating each group of ganged switches all to closed condition, and means for selectively disabling arrays of switches selected one from each group.

llll. The combination according to claim 10, wherein is provided two buses, a first of said buses supplying lamp energizing voltage of a smaller magnitude and a second of said buses supplying lamp energizing voltage of a larger magnitude, means for connecting a plurality of said lamps to said second of said buses each via one of said switches, and via an impedance such as to reduce the voltage across each energized lamp to said smaller magnitude, and means for connecting said last-mentioned lamps to said first of said buses selectively via one of said switches and via substantially zero impedance.

12. In an electric organ employing key-controlled tone generators, each of said tone generators including a lamp fully energized in response to a predetermined flow of current I therein, a first key-operated switch, a second key-operated switch, a first source of relatively low voltage E, a second source of relatively high voltage E a resistance of value R, where IR=E E means connecting one of said lamps in a series circuit including said first source of voltage and said first key-operated switch, and means connecting another of said lamps in a series circuit including said second source of voltage, said second key-operated switch and said resistance.

13. The combination according to claim 12, wherein said key-operated switches are ganged.

14-. The combination according to claim 13, wherein is provided a further circuit for at will energizing said another of said lamps via a path of zero impedance from said first source of voltage and said second switch.

15. In an electronic organ, a pitch disc of insulating material containing a plurality of concentric recorded pitch tracks, means for rotating said pitch disc in full atmosphere, a stationary conductive plate subsisting parallel to and immediately adjacent to said pitch disc, said conductive plate included apertures located for enabling illumination of said pitch tracks selectively, said pitch disc and said plate being subjected to dust in said atmosphere, whereby dust collects on said pitch disc while said pitch disc is stationary, the speed of rotation of said pitch disc being sufficiently high to generate a potential gradient radially of said pitch disc and between the outer circum- .21 ference of said pitch disc and said conductive plate of magnitude adequate to remove said dust from said pitch disc and to deposit same on said plate.

16. In a keyed photoelectric organ wherein is provided a plurality of tone generators, at least one for each tone of a plurality of octaves, and wherein each tone generator includes a lamp which effects generation of a tone only when energized, the combination of a photocell for receiving light passing through said generators from said lamp, means for switching the light from each of said lamps to said photocell on and oil, each of said switch means pertaining to a note of a predetermined nomenclature in a specified octave, means for ganging groups of said switch means having the same nomenclature, a plurality of keys, each for actuating each of said groups to an on condition, and means for selectively disabling arrays of said switch means selected one from each of said groups.

17. In a keyed musical instrument, a record storing device, said record storing device having recorded thereon a plurality of re-entrant tracks each corresponding with a complex musical tone, a plurality of adjacent ones of said tracks having the same nomenclature in different octaves, a multiplicity of said adjacent tracks being provided for different nomenclatures, first means for at will selecting and reproducing the musical content of any of said tracks as first electrical signal in a first channel, second means for at will reproducing the musical content of any of said tracks as second electrical signal in a second channel, and means for commonly acoustically reproducing the signal content of both said channels.

18. A sound storage record for a key-controlled electronic musical instrument, comprising a first plurality of light modulating immediately adjacent sound tracks on said record, each of said immediately adjacent sound tracks pertaining only to first harmonically related tones of a first nomenclature, a second plurality of light modulating immediately adjacent sound tracks on said record, each of said immediately adjacent sound tracks pertaining to second harmonically related tones of only a second and different nomenclature, and a gap intermediate said first and second pluralities of immediately adjacent sound tracks.

19. The combination according to claim 18, wherein is provided means responsive to a single key for selecting and reproducing the musical content of two different ones of said tracks.

20. A system for reproducing signals comprising a reentrant sound carrying track record having a plurality of light modulating tracks of the same musical nomenclature but of diifering octaves, several of said plurality of tracks being provided on said record for different musical nomenclatures, a first photoelectric cell, a second photoelectric cell, a first source of light for each of said tracks, a second source of light for each of said tracks, each of said sound tracks being interposed between its respective first source of light and said first photoelectric cell, each of said sound tracks being interposed between its respective second source of light and said second photoelectric cell, first formant filter means connected with said first photoelectric cell for modifying at will the tonal characteristics of first signal generated by said first photoelectric cell, second formant filter means connected with said second photoelectric cell for modifying at will the tonal characteristics of second signal generated by said second photoelectric cell, and means for combining the first and second signals as modified by said formant filter means.

21. In a system for reproducing musical signals recorded on a single re-entrant sound record having a plurality of tracks of the same musical nomenclature but of difiering octaves, several of said plurality of tracks being provided on said record for differing musical nomenclatures, means in first and second channels for reproducing said musical signal from said sound track,

22 separate formant filters in each of said channels for independently modifying the tonal character of the musical signals in said channel and means for combining and reproducing the modified musical signals.

22. An assembly for reproducing tones at will comprising a multi-track tone disc having a plurality of light modulating .re-entrant tracks, a plurality of said tracks being harmonically related and of the same musical nomenclature, several of said plurality of tracks being provided for differing nomenclatures, means for rotating said disc about its center, a slit plate located in a plane parallel to said tone disc, an arm of lamps arranged in a plane parallel to said slit plate, said slit plate lying between said tone disc and said array of lamps, at least one lamp and at least one slit being operatively and individually associated with each track of said multi-track tone disc, at least one photocell for receiving light emanating from each lamp, passing through the at least one slit associated with the last-mentioned lamp and modulated by the track associated with the last-mentioned lamp, wherein the radial distances of said photo-cell, said track, said slit and each of said lamps are of increasing magnitude in the order of recitation, said photo-cell being a finite radial distance from the disc center, the positions of each one of said lamps, the track responsive to a particular lamp and said slit plate are expressed as:

where R -zradial distance from the disc center to said particular lamp;

A=distance from said slit plate to said particular lamp;

B=shortest distance from the photocell to said slit plate;

T=radial distance from the disc center to the particular track =radial distance from the disc center to the photo-cell;

and

=angle between the lamp radial and the photo-cell axis plane.

23. In combination, a photocell, a modulating element having a plurality of re-entrant harmonically related tracks, each corresponding with the same musical nomenclature, a multiplicity of said plural tracks on said element corresponding with notes of difiering nomenclature, a light beam defining device having a slit and a source of light, all in a single plane and lying in a first rectilinear line from which may be drawn plural perpendiculars to a second rectilinear line, said perpendiculars to said photocell, said modulating element, said slit and said source of light lying at progressively increasing distances from said second rectilinear line.

24. A system for reproducing audio signals in a space having the shape of a circular cylinder, said circular cylinder having an axis and a bisecting plane passing through said-axis to define two sub-spaces, two photocells each in a different one of said sub-spaces, an opaque member lying generally in said bisecting plane between said photocells, a light modulating pitch disc rotatable on said axis and having a plurality of re-entrant harmonically related tracks, each corresponding with the same musical nomenclature, a multiplicity of said plural tracks on said member corresponding with notes of difiering nomenclature, each of said tracks being at different radial distance from said axis and symmetrical with said axis, a slit disc having two slits for each of said tracks, each of said two slits being located in a different one of said sub-spaces, a plurality of light sources each individual to each of said slits, and means for energizing said lights selectively, the two slits for each of said tracks always being positioned to permit light from its responsive source to impinge on its respective photocell, said photocells, pitch disc, slit disc and sources of light lying in planes 2? perpendicular to said axis arranged in the order last stated along said axis.

25. The combination according to claim 24, wherein each of said photocells, and each pitch track, each slit and each light source which cooperates to apply a modulated light beam to a photocell are at progressively increasing radial distances from said axis.

26. The combination according to claim 25, wherein is further provided a separate pre-amplifying channel connected to each of said photocells, different formant filters in each of said channels, and a common power amplifier coupled to both said channels.

27. In an electronic organ, a pitch disc of insulating material containing a plurality of concentric recorded pitch tracks, a stationary conductive plate subsisting parallel to and immediately adjacent to said pitch disc, said conductive plate included apertures located for enabling illumination of said pitch tracks selectively, said pitch disc and said plate being subjected to dust in said atmosphere, whereby dust collects on said pitch disc while said pitch disc is stationary, means for rotating said disc in full atmosphere at an angular velocity sufliciently high to generate a potential gradient radially of said pitch disc and between the outer circumference of said pitch disc and said conductive plate of magnitude adequate to remove said dust from said pitch disc and to deposit same on said plate. i

28. The organ of claim 27 including means for connecting the conductive plate to ground potential.

, ag Q .1 References Cited by the Examiner UNITED STATES PATENTS 1,167,663 1/16 Sinclair et al.

2,014,528 9/35 Keller 274-42 2,033,232 3/36 Eremeefr' 841.18 2,038,976 4/36 Wood et al 274-41 2,169,842 8/39 (annenberg 841.18 2,220,488 11/40 Lott 179100.3 2,243,090 5/41 Dudley 274-41 2,373,960 4/45 Huenlich 274-47 2,469,850 5/49 Spielman 841.l8 2,473,897 6/49 Miller 841.28'X 2,484,914 10/49 Spielman 841.18 2,540,285 2/51 Phillips 841.18 2,545,469 3/51 Jordan 25036-7.6 2,563,647 8/51 Hammond 179100.3 2,571,141 10/51 Knoblaugh et a1 841.18 2,574,577 11/51 Martin et al. 250367.6 2,582,939 1/52 Frederick 274-47 2,754,713 7/56 Bajolet 841.18 2,830,481 4/58 Hanert 841.01 2,842,021 7/58 Oncley 841.01 2,897,710 8/59 Lemoine 84-1.28 2,924,138 2/60 Jones 84-128 2,946,253 7/60 Clark 84-1.18 2,977,584 3/61 Siegel.

- ARTHUR GAUSS, Primary Examiner.

CARL W. ROBINSON, Examiner. 

2. IN A KEYED MUSICAL INSTRUMENT, A SINGLE RECORD STORING DEVICE, SAID RECORD STORING DEVICE HAVING RECORDED THEREON A PLURALITY OF RE-ENTRANT TRACKS EACH CORRESPONDING WITH A COMPLEX MUSICAL TONE, CERTAIN OF SAID TRACKS BEING NON-HARMONICALLY RELATED, FIRST MEANS FOR AT WILL SELECTING AND REPRODUCING THE MUSICAL CONTENT OF ANY OF SAID TRACKS AS FIRST ELECTRICAL SIGNAL IN A FIRST CHANNEL, SECOND MEANS FOR AT WILL REPRODUCING THE MUSICAL CONTENT OF ANY OF SAID TRACKS AS SECOND ELECTRICAL SIGNAL IN A SECOND CHANNEL, AND MEANS FOR COMMONLY ACOUSTICALLY REPRODUCING THE SIGNAL CONTENT OF BOTH SAID CHANNELS. 